A conventional instrument for measuring temperature by use of a thermocouple is provided with a terminal block to which ends of the thermocouple, on one side thereof, are connected. The terminal block is provided with a plurality of pairs of terminals to which signal lines of the thermocouple are connected, respectively, thereby feeding detection signals transmitted via the respective terminals to measurement means inside the instrument.
With this terminal block, as the number of the terminals provided increases, so does the size of a block surface, and the terminal block becomes more susceptible to external thermal effects of an environment in which the terminal block is installed. Because this can affect the detection signals transmitted via the respective terminals, there is the need for making temperature compensation for the detection signals upon measurement.
Accordingly, the terminal block is made up such that a terminal block temperature detection sensor for detecting the temperature of the terminal block itself is provided therein, and a temperature compensation signal as detected by the terminal block temperature detection sensor is fed to a compensation circuit, thereby compensating for the detection signals transmitted via the respective terminals.
As to the related art concerning a temperature-measuring device using a thermocouple, the following Patent Documents are well known.    [Patent Document 1] JP 05-164628 A    [Patent Document 2] JP 2001-74564 A
FIG. 7 is a front view showing an example of an input terminal block of a temperature-measuring device capable of measuring respective temperatures of 10 channels (spots). In the figure, reference numeral 1 denotes a substrate rectangular in shape, having a metal plate, and 10 pairs of contact terminals are attached to the substrate in such a way as to be arranged in parallel in the longitudinal direction of the substrate. Reference numeral 3 denotes a thermocouple composed of two dissimilar metal wires, having ends on one side thereof, joined with each other, and the other ends connected to one pair of the contact terminals 2 (hereinafter referred to merely as terminals), respectively (in the figure, only one spot is shown). Reference numeral 4 denotes a temperature sensor constituting a reference junction compensation circuit provided substantially at the central part of the substrate 1.
FIG. 8 is a front view showing a temperature-measuring device for 30 channels, composed of 3 units of the temperature measuring devices shown in FIG. 7, disposed in series, each serving for 10 channels. That is, one unit of the temperature sensor 4 constituting the reference junction compensation circuit is installed for every 10 channels.
Now, in the case of a temperature-measuring device capable of measuring temperature with a thermocouple, there is normally the need for one unit of the temperature sensor for every channel. In reality, however, with the temperature measuring device for on the order of 10 channels, the need is met with one unit of the temperature sensor by using a substrate having a metal plate, or introducing a novel idea into a mechanical design, thereby satisfying a product specification.
FIG. 9 is a front view showing the case where a multichannel temperature-measuring device for 30 channels is incorporated in a substrate having one sheet of metal plate. In such a case, the width of the device is enlarged, so that there is a possibility of occurrence of variation in temperature distribution in the x-axis (transverse) direction of an input terminal block due to heat evolved at modules 5a, 5b, fitted to respective sides of the device. For this reason, there arises the need for one unit of the temperature sensor for every 10 channels. In the figure, regions indicated by A of input terminals, on respective sides of the input terminal block, are prone to be affected by heat evolved at the modules 5a, 5b, fitted so as to be adjoined to the respective regions A, while input terminals in a region indicated by B are subjected to the effects of heat of the input terminals, on the respective sides thereof, thereby undergoing a change, respectively.
However, there has existed a problem from the viewpoint of cost reduction in that it is difficult to achieve reduction in cost if 3 units of the temperature sensors are used for a temperature-measuring device for not less than 30 channels, as in the past case, because the temperature sensor is high in cost.